Spraying device



May 22, 1928. 1,670,711

H. BRYAN ET AL SPRAYING DEVI CE Filed April 15, 1927 INV ENT [IRE HARRY BRYAN WILLIAM H Hl: E E

RICHARD ADAMS WITNEEEEE Za ATT DRNEYE Patented May 22, 1928.

UNITED STATES 1,670,711 PATENT ori-"ice,

HARRY BRYAN, WILLIAM H. ROSS, AND. JAMES RICHARD ADAMS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNORS TO TI-IE GOVERNMENT AND THE PEOPLE 0F THE UNITED STATES 0F AMERICA.'

SPRAYING DEVICE.

Application led April 13, 1927. Serial No. 183,524.

(GRANTED UNDER THE PROVISIONS 0F THE ACT 0F MARCH 3, 1883, 22 STAT. L., 625.)

This application is made under the act of March 3. 1883. chapter 143 (2Q Stat. 625) and the invention herein described and claimed may be used by the Government of the United States or any of its ofiicers or employees-in the prosecution of work for thev Government, or by any citizen of the United States, without payment to us of any royalty thereon.

Commercial fertilizers as now manufactured consist of mixtures of inorganicl salts and of various organic wastes such as cotton seed meal, tankage and fish scrap. These organic materials are admirably suited for use in fertilizers in that they not only serve as importantsources of plant food but they also greatly improve the physical condition of the mixture in which they are included. The supply of these materials is not sufficient, however, to meet the demand and the proportion in which they now occur in fer-v tilizers is estimated to be only about half as great as a few years ago. With ay view to supplying this deficiency in nitrogenous materials a great deal of attentionvis now being given to the synthesis of such nitrogen compounds as calcium nitrate, urea and ammonium nitrate.

From a chemical point of view, these materials are particularly well adapted for use as fertilizers. They together contain the three forms of nitrogen-ammonia, nitrate and organic-which are considered desirable in all mixed fertilizers; they leave no accumulat-ion of toxic residues in the soil; and all contain nitrogen in a readily available form.

It unfortunately happens, however, that these. salts are all hygroscopic and readily absorb moistureA from the air at humidities which commonly prevail in humid countries. This property greatly interferes with their use in fertilizers in that it causes the mixture in which they are included to become sticky and cake. The principal cause of caking in salts of this kind is due to a knitting together of the-crystals by the successive absorption and loss of moisture when the humidity of the air alternately rises above and then falls below that corresponding to the vapor pressure of their saturated solutions. The rate at which setting occurs will necessarily vary greatly with the mechanical condition of the material and will be .most pronounced in products which are finely ground. In this condition the points' of contact between the individual particles are at a maximum. the surface area of the material is relatively large, the force of adhesion acting between the very fine particles is considerable, and a secondary knitting occurs through thc growth of the larger crystals at the expense of the smaller crystals. This exchange of crystal growth is duc to the difference in solubility of crystal particles which differ in size as necessarily occurs in all materials that have been pulverized by grinding.

`We have found that the physical condition of a fertilizer material may be greatlyimproved when it is prepared in the form of spherical halls or grains of uniform size. In this condition the surface area of the material is greatly reduced-the points of contact between the individual particles are at a minimum, the force of adhesion no caking which depends on wide variations in' the size of the particles is entirely prevented.

The granulation of a. fertilizer material in the form of spherical balls or grains gives it the further distinctive property of readilv flowing through an oriice or through the adjustable openings in a fertilizer drilling or distributing machine.

In the preparation of urea from ammonia and carbon dioxide the liquefied gases are compressed into an autoclave at about 100 atmospheres and 135 C., and the resultant 'liquid product allowed to discharge through a relief valve at the topof the autoclave into a fractionating column lto separate the uncombined ammonia and carbon dioxide from the solution of urea which is formed inthe process. The latter is then concentrated in a vacuum evaporator and the molten prod-" the molten threaded connection through such conditions that the droplets congeal to solid spheres before reaching the bot-tom of the spraying chamber. The necessity for subsequent crushing or grinding of the ureaV ability and reduce the cost of manufacturc.

In the' accompanying drawings there is shown one embodiment of an apparatus for carrying out the process of our invention.

Fig. 1 is a vertical sectional view through the spraying chamber and the compartment above the chamber in which the evaporators are shown in elevation.

Fig. 2 is an enlarged vertical cross-sectional view of the spraying device used in our process.

Fig. 3 is a horizontal cross-sectional view of the spraying device taken on the line 3-8 of Fig. 2, and,

Fig. 4 is a bottom plan view of the angular valve of the spraying dcvice-the hollow shaft being shown in cross section.

Referring to the drawings,^1 represents vacuum evaporators or other containers in which a solution of urea, calcium nitrate or other fusible material is evaporated to such a concentration that its content of water is reducedto 10 per cent or less. The evaporators are connected at the bottom through the valves 2, the steam-jacketed pipe 3 and the flanged T 4 with a common outlet pipe 5.

The pipe 5 opens into the spraying device 6 which is centrally located at the top of the spraying chamber 7. The lower portion of the spraying chamber is constructed in the form of a series of hoppers 8 in annular arrangement about the pipe 9. The walls of the hoppers converge downwardly and the lower end of each is provided with a spout 10 and a valve 11 of any suitable design.

Circulation of air through the vspraying chamber is secured by means of a fan 12 which continuously withdraws air at ordinary temperature and pressure through the inlet 13, or treated air from a conditioning system, not shown, through the inlet 14,ac cording as the two-way valve 15 is set to receive one or the other, and forces it through the pipe 9, the spraying chamber 7 and the exit openings 16.l

The spraying device as shown in the crosssectional views of Figs. 2, 3 and 4, consists of a rotatable cylinder 1 7 mounted on a hollow shaft 18 which is provided with a collar 19 and is supported within the cast iron bushing 2Q by the thrust bearing 21 and the roller bearing 22.

The cylinder 'is mounted on the shaft by the tapped boss' 23. The portion of the shaft which extends vi' `n the cylinder is slotted vertically to form he segmented annular sections `24. These -slots serve as guides for the crossarms 25 of the annular shaped float 26 which is free to move up and down within the cylinder. A connectingQrod 2 7 which is mounted on the float 26 supports a GO degree angular valve 28 within the hollow shaft 18. The lower end of the outlet pipe 5, which dips into the hollow shaft 18, is beveled at 29 to serve asa seat for the valve 28. The latter is held in a central position by the rim 30 which is grooved in a vertical direction to form openings 31 for the free passage ofv liquid through the shaft.

The cylinder of the spraying device .may be conveniently constructed in two sections which are held together at theirlangcd edges 32 by machine bolts This arrangement of parts offers the advantages that it provides struction and .one that can be readily disassembled for cleaning or repair. Y The llower section of the cylinder is provided with equally spaced perforations 34 which extend in one or more horizontal rows around the cylinder. Tbedesired speed of rotation of the cylinder around its axis is secured by the variable speed motor 35 which acts through the bevel gears 36. Y lnthe operation of the process the material to be granulated is concentrated or fused in one of the evaporators while being sprayed from the other. The valve 2 at the bottom of the evaporator is then opened and the solution allowed tovdischarge by gravity flow through the pipe 5 into the hollow shaft au d cylinder of the .spraying device. In the construction of the apparatus the size and number of the perforations are so adjusted that the outow from the rotating cylinder is less than the minimum unobstructed inflow through the pipe 5. The spraying device accordingly quickly fills with solution to the point where the float in the cylinder is buoyed up by a force which just balances the pressure on the valve 28 due to the head of solution at the outlet of pipe 5. As the inflow of solution from pi e 5 tends to increase or decrease the resulting rise and fall of the `level of solution in he hollow shaft 18 brings about a corresponding rise and fall of the valve 28 which offsets any tendency te change in the volume ofiniiow. The purpose of the float and valve is thus to provide any automatic means for maintaining a uniform flow of solution through the apparatus throughout the periodxof spraying.

Therotation of the cylinder is adjusted to such a speed that the solution is broken up into small droplets by. centrifugal force as it issues from the perforations of the cylinder in a horizontal direction. The droplets are congealed as they' fall through'the chamber by a counter-current flow of air and are an apparatus of simpleconf collected in the hoppers 8 in the form of spherical particles of uniform size.

The size of the particles varies with the' speed of rotation of thecylinder, the crosssectional area of the iridividual perforations and with the density and surface tension of the solution sprayed. It has been found that when the speed of rotationof the cylinder and the size of the perforations are properly adjusted it is possible to spray a material so that 90 per cent will pass through a 20 mesh and be retained in a 30 mesh screen. Any change in the speed of rotation Will be followed by a marked change in the uuiformity of the sprayed particles.

If the material to be sprayed is of a hygroscopic nature it is necessary to reduce the relative humidity of the air in the spraying chamber below that corresponding to the vapor pressure of its saturated solution. This can be secured most economically by passing the air through a spray chamber operated in connection with a refrigerating plant to condense out the necessary amount of Water. In the case of calcium nitrate, for example, the vapor pressure of its saturated solution corresponds to a relative humidity of 55 per cent ata temperature of 20o C.

This means that calcium nitrate will deliquesce when exposed to air having a relative humidity above 55 per cent and itl is therefore necessary to reduce the relative humidity of the air in the spraying chamber below this percentage When spraying a ma terial of this kind.

The temperature to Which the spraying Water used in cooling the air must be reduced to give any desired relativehumidity at a given temperature may be found by use lof a psychrometric chart such as that given by W. H. Carrier in the Trans. Am. Soc. Mech. Engrs. 33, 1005 (1911). This chart shows that if it is desired to reduce the relative humidity ot the air to, say, 45 per cent at 20o C., the -temperature of the water used in the spray through which the air is passed must be reduced to 7o C. If the relative humidity of the air is already belou7 45 per cent no treatment is then necessary and ordinary air may then be introduced into the spraying chamber through the inlet 14.

While the foregoing description of the process of our invention refers particularly to the granulation of a fused material, it is to be understood that our invention is equally applicable for spraying the solution of a salt for the purpose 0f dehydratingit.

When this is the object of .the process het.;

the inflow of the fused material into the spraying device at a rate equal to the outiow.

HARRY BRYAN. WILLIAM H. ROSS. JAMES RICHARD ADAMS. 

